It all began with the fact that KSM works only on memory that is marked
by madvise(). And the only way to get around that is to either:
* use LD_PRELOAD; or
* patch the kernel with something like UKSM or PKSM.
(i skip ptrace can of worms here intentionally)
To overcome this restriction, lets employ a new remote madvise API. This
can be used by some small userspace helper daemon that will do auto-KSM
job for us.
I think of two major consumers of remote KSM hints:
* hosts, that run containers, especially similar ones and especially in
a trusted environment, sharing the same runtime like Node.js;
* heavy applications, that can be run in multiple instances, not
limited to opensource ones like Firefox, but also those that cannot be
modified since they are binary-only and, maybe, statically linked.
Speaking of statistics, more numbers can be found in the very first
submission, that is related to this one [1]. For my current setup with
two Firefox instances I get 100 to 200 MiB saved for the second instance
depending on the amount of tabs.
1 FF instance with 15 tabs:
$ echo "$(cat /sys/kernel/mm/ksm/pages_sharing) * 4 / 1024" | bc
410
2 FF instances, second one has 12 tabs (all the tabs are different):
$ echo "$(cat /sys/kernel/mm/ksm/pages_sharing) * 4 / 1024" | bc
592
At the very moment I do not have specific numbers for containerised
workload, but those should be comparable in case the containers share
similar/same runtime.
[1] https://lore.kernel.org/patchwork/patch/1012142/
Signed-off-by: Oleksandr Natalenko <oleksandr@xxxxxxxxxx>
---
mm/madvise.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/mm/madvise.c b/mm/madvise.c
index 84f899b1b6da..e8f9c49794a3 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -991,6 +991,8 @@ process_madvise_behavior_valid(int behavior)
switch (behavior) {
case MADV_COLD:
case MADV_PAGEOUT:
+ case MADV_MERGEABLE:
+ case MADV_UNMERGEABLE:
return true;
default:
--
2.22.0
